Device for carrying out observations of an image formed on an image forming surface



Sept. 30, 1969 HIROSHI AMOH 3,469,909

DEVICE FOR CARRYING OUT OBSERVATIONS OF AN IMAGE FORMED ON AN IMAGE FORMING SURFACE Filed Dec. 26. 1967 .2 Sheets-Sheet 1 INVENTOR HIRDJl-H PHD/l BY I ATTORNEY 5 pt. 30. 1969 I HIROSHI AMOH 3,469,909

DEVICE FOR CARRYING OUT OBSERVATIONS OF AN IMAGE FORMED ON AN IMAGE FORMING SURFACE Filed Dec. 26, 196'? .2 Sheets-Sheet 2 ATTORNEYS United States Patent 3,469,909 DEVICE FOR CARRYING OUT OBSERVATIONS OF AN IMAGE FORMED ON AN IMAGE FORMING SURFACE Hiroshi Amoh, Tokyo, Japan, assignor to Ushio Electric Inc., Tokyo, Japan Filed Dec. 26, 1967, Ser. No. 693,659 Claims priority, application Japan, Dec. 30, 1966 (utility models), 42/559, 42/560 Int. Cl. G03b 21/28 US. Cl. 353-98 1 Claim ABSTRACT OF THE DISCLOSURE A device for carrying out observation of an image formed on an image forming surface. The device has a pattern plate to be projected, a work piece having an image forming surface thereon and an image forming lens. The lens projects symbols of the pattern plate and forms an image thereof on a reduced scale on the image forming surface. A light beam divider is provided in the path of light between the pattern plate and the image forming lens. The light beam divider is tilted with respect to the path of light and movable eyepieces are provided for observing on an enlarged scale the details of the image reflected from said light beam divider.

This invention relates to a device for carrying out observations of an image formed on an image forming surface of a work piece of a desired pattern projected on a reduced scale on said image forming surface for printing thereon in the art of microphotographic printing.

Generally, in the art of microphotographic printing, patterns formed on a plurality of pattern plates which make up a set are successively printed on a reduced scale on a work piece by accurately and precisely effecting focusing and positioning of the patterns on the work piece by means of a lens. In one method of carrying out observations of an image formed on an image forming surface of a work piece known in the art of microphotographic printing, a light beam divider such as a transparent mirror tilted at an angle of 45 degrees, for example, is arranged between a subject and a lens so as to take the light reflected from the image forming surface out of the system to permit the operator to carry out observations of the image formed on the same scale as the subject. According to this method, observations of the image formed on the same scale on the image forming surface of the pattern of each pattern plate which is the subject are carried out by watching, with naked eyes or by using fixed eyepieces, the image taken out of the system by means of the light beam divider to be projected on frosted glass.

In the process of producing semiconductor elements, for example, it is required that positioning of a series of patterns of a set of pattern plates be effected with an allowable error of about 1 micron or less on a base crystal on which the images are formed. Moreover, it is required that the images of all the patterns formed on the base crystal be correctly focused with respect to all the portions thereof. When the aforementioned prior art method of observations is used, however, difficulty has been met with in accurately effecting focusing and positioning of the patterns over a wide area.

In an apparatus for carrying the aforementioned method into practice, the property of an image forming lens used and the rate of reduction of an image formed from a subject make itnecessary to arrange a pattern plate and the image forming lens to be spaced apart from each other a substantially large distance. With this arrangement, the surface on which an image is projected by the light beam divider and the surface on which an image is formed by the image forming lens are spaced apart from each other a substantially large distance, making it practically impossible to simultaneously effect fine adjustments of these two surfaces accurately and precisely. Thus, it has hitherto been difiicult to obtain products which are satisfactory for specifications and orders in precision.

A lens having a high resolving power is generally designed to exhibit good characteristics with a light beam of particular wavelength. In microphotographic printing, a light source is arranged or a special filter device is used in such a manner as to cause only the light beam of this wavelength to pass through the lens. Generally, a color filter is arranged over the light beam divider or the light beam divider is removed to use a color filter. Mounting and removing the color filter and the light beam divider have hitherto involved troublesome time-consuming operational steps.

With a view to obviating the aforementioned disadvantages of prior art method, the present invention has been made.

Accordingly, one object of the present invention is to provide a device for carrying out observations of an image formed on an image forming surface which enables carrying out observations, over a wide area by means of movable eyepieces, of an image of a subject formed on an image forming surface in order to accurately effect focusing and positioning of the image.

Another object of the invention is to provide a device for carrying out observations of an image formed on an image forming surface in which an image forming surface and a surface on which the light reflected by said image forming surface is projected to permit the observer to carry out observations of the image on the image forming surface are spaced apart from each other 'a substantially smaller distance than in a prior art device.

Still another object of the invention is to provide a device for carrying out observations of an image formed on an image forming surface which is constructed such that only the light beam of a particular wavelength is permitted to pass through an image forming lens without requiring the operational steps of mounting and removing a light beam divider and a filter.

Other objects and features of the present invention will become apparent from consideration of the following description in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view showing one embodiment of the device according to this invention;

FIG. 2 shows, on an enlarged scale, an image projected on a surface for carrying out observations of the image on an image forming surface; and

FIG. 3 is a schematic view showing another embodiment of the device according to the present invention.

In FIG. 1, 10 designates a pattern plate on which a large number of symbols are formed to be projected onto an image forming surface, and 11 is an image form- 'ing lens which preferably is a monochromatic lens having a high resolving power and operating in a single wavelength. 12 designates a work piece such as a semi-conductor element, for example, having thereon an image forming surface 13 on which the image of the symbols of the pattern plate 10 is formed on a reduced scale by means of said image forming lens 11. The position of said work piece 12 can be minutely adjusted in all the directions along the axes x, y and z by means of a fine adjustment (not shown). A light beam divider 14 is inserted in the path of light between said pattern plate 10 and said image forming lens 11 in such a manner as to be tilted at an angle of 45 degrees with respect to the path of light, said light beam divider permitting the light beam from said pattern plate to pass therethrough but reflecting the light beam reflected by the image forming surface 13 and passing through the image forming lens 11. In the embodiment of the invention illustrated, a transparent mirror is used as the light beam divider 14. A surface 15 has projected thereon the image of the symbols of the pattern plate 10 reflected by the light beam divider 14. Eyepieces 16 permit the observer to carry out observations of an enlarged image of the symbols projected on said surface 15. The eyepieces 16 are mounted on a supporting frame member 17 and disposed at a position opposite to the light beam divider 14 with respect to said surface 15. The longitudinal frame members 18 have grooves 19 in which said supporting frame member 17 is slidably supported. The transverse frame members 20 have grooves 21 in which said longitudinal frame members 18 are slidably supported. The horizontal frame members 22 have grooves in which said transverse frame members 20 are slidably supported. Though not shown, the supporting frame may be formed with grooves for supporting the eyepieces 16 therein so that the distance between the two eyepieces 16 may be varied as desired when it is required to do so.

The manner in which observations are carried out by using the illustrated embodiment of the device according to this invention will now be explained. Upon placing the pattern plate 10 having a large number of symbols A formed thereon at a predetermined position, an image on a reduced scale of the symbols A of the pattern plate 10 is formed through the image forming lens 11 on the image forming surface 13. At the same time, the light reflected by the image forming surface 13 is cast by the light beam divider 14 on the frosted glass 15 on which an image of the symbols A is formed on the same scale as the symbols A on the pattern plate 10. In effecting focusing of the symbols A of the pattern plate 10, the position of the work piece 12 is adjusted by means of a fine adjustment (not shown) while the observer is looking through the eyepieces 16 in such a manner that the image forming surface 13 can be seen clearly and a scale of the unit length disposed in the same plane as the pattern plate 10 can have the same length in the image formed on the image forming surface 13. After the aforementioned adjustment has been effected satisfactorily, exposure of the image formed on the image forming surface 13 is effected properly whereby the symbols A of the pattern plate 10 can be printed on said surface on a reduced scale. In printing another group of symbols B on the same image forming surface in superimposing relation with respect to the symbols A, the symbols B should be correctly positioned relative to the symbols A. To accomplish this end, the pattern plate 10 is replaced by another pattern plate 10 having the symbols B formed thereon, which is placed at a predetermined position, and the observer watches the image of symbols B formed on the frosted glass 15 through both the right and left eyepieces 16 at the same time or one at a time while operating the aforementioned fine adjustment to move the work piece 12 to adjust its position with respect to the angle of direction 0 as well as the vertical direction (z axis) and horizontal direction (x and y axes) so that the symbols B may be correctly positioned relative to the symbols A. In the semi-conductor element industry, for example, it is required that positioning of the symbols with respect to one another be effected to the accuracy of -1 micron over the entire surface when the pattern plates 10 and 10' are 10 cm. x 10 cm. in size. In order to effect adjustments within this tolerance, the eyepieces 16 are first put at a position where the image as seen through the eyepieces is as shown at No. 1 position in FIG. 2. With the eyepieces 16 at this position, the observer operates the fine adjustment as aforementioned to bring the symbols A and B into their correct positions relative to each other. Then, the eyepieces 16 is moved horizontally by moving the longitudinal frame members 18 in sliding motion in the grooves 21 of the transverse frame members 20 to a position where the image as seen through the eyepieces is as shown at No. 2 position in FIG. 2. With the eyepieces 16 at this second position, the observer operates the fine adjustment as aforementioned to bring the symbols A and B into their correct positions relative to each other. Thus, the eyepieces 16 are brought successively to a third and a fourth position so that the symbols A and B may be brought to their correct positions relative to each other over the entire surface. It is to be noted that when the distance between the two eyepieces 16 is increased, the symbols A and B can be more accurately positioned relative to each other. It is further to be noted that, although the accuracy of positioning varies depending on the property and magnification of the lens used, positioning can be effected within the tolerance of 1 micron if a lens of 500 magnifications or more is used.

Another embodiment of the device according to the present invention will now be explained with reference to FIG. 3. In this embodiment, the image forming surface on which an image of a number of symbols is formed by the image forming lens 11 and the surface 15 on which the image of the symbols formed on the image forming surface is projected is spaced apart a particularly smaller distance than in the prior art device in order to facilitate the adjustment of the position of work piece 12 while watching the image of symbols projected on the surface 15. It will be noted that the light beam divider 14 is disposed nearer the image forming lens 11, that a reflector 23 is mounted in opposed relation to said light beam divider 14 so as to reflect the light from the light beam divider 14 in a direction different from the direction of movement of the light beam from the divider, and that another reflector 24 is mounted in opposed relation to said reflector 23 so as to reflect the light beam the reflector 23 in a direction different from the direction of movement of the light beam from the reflector 23. Additional reflectors may be mounted in the same way if necessary. Thus, the space between the pattern plate 10 and the light beam divider 14 which covers a distance I is divided in such a manner that the distance I is equal to the sum of the distance 1 between the light beam divider 14 and the first reflector 23, the distance 1 between the first reflector 23 and second reflector 24, and the distance I between the (nl) the reflector and the surface 15. This arangement enables to substantially reduce the distance between the image forming surface 13 on which an image is formed by the image forming lens 11 and the surface 15 on which the image formed on the image forming surface 13 is projected. This feature makes it possible to promptly and accurately adjust the position of the work piece 12 by operating the fine adjustment in accordance with the information on focusing and positioning obtained through the image projected on the surface 15 by the light beam divider 14, thereby increasing the accuracy of focusing and positioning operations.

Preferably, the light beam divider 14 illustrated in the embodiments shown in FIGS. 1 and 3 is a colored transparent mirror which permits only the light beam of the same wavelength as the light beam which is permitted to pass through the image forming lens 11 to pass therethrough. The use of such light beam divider not only simplifies the operational steps because the trouble of mounting a colored filter over the light beam divider or substituting a colored filter for the light beam divider can be obviated, but also can prevent a disturbance due to a change in effective length of a light path which occurs when the light beam divider is replaced by a colored filter. The arrangement permits to continue with the operation of the optical system without varying the length of its light path. Thus, with this arrangement, satisfactory results can be achieved in effecting precision focusing of a number of minute symbols of 10 micron or less in size.

It is to be understood that the form of the invention herewith shown and described is to be taken as preferred embodiments. Various changes may be made in the shape, size and arrangement of parts. For example, equivalent elements may be substituted for those illustrated and described herein, parts may be reversed, and certain features of the invention may be utilized independently of the use of other features, all without departing from the spirit or scope of the invention as defined in the subjoined claim.

What is claimed is:

1. A device for carrying out observations of an image formed on an image forming surface comprising a pattern plate to be projected, a work piece having an image forming surface thereon and spaced from said pattern plate in opposed relation, an image forming lens for projecting a number of symbols of said pattern plate and forming an image thereof on a reduced scale on said image forming surface of said Work piece, a light beam divider inserted in the path of light between said pattern plate and said image forming lens and tilted with respect to said path of light, said light beam divider comprising a filter which permits only the light of the same wavelength as the light permitted to pass through said image forming lens to pass therethrough, said light beam divider permitting the light beam from said pattern plate to pass therethrough but reflecting the light beam from the image forming surface on the work piece, at least one reflector for reflecting the light beam from said light beam divider, and a surface on which the light reflected by said reflector is cast for observations.

References Cited UNITED STATES PATENTS 774,656 11/1904 Donnan. 2,427,256 9/ 1947 Butscher. 2,493,558 l/ 1950 Thompson.

FOREIGN PATENTS 804,654 11/ 8 Great Britain.

NORTON ANSHER, Primary Examiner ROBERT P. GREINER, Assistant Examiner 

